Nickel-Cobalt Vein Deposits

Open fractures is where these vein deposits are shaped and formed. They can be in whatever number of different host rocks, even though they are more common in crystalline metamorphic rocks, granitic sediments and intrusions. These deposits are very rare in volcanic rocks. They contain cobalt and nickel arsenides and possibly can contain native silver, argentite,, pitch-blende, pyrite, chalcopyrite, sphalerite and galena; the gangue is any or all of dolomite, calcite and quartz. Here are some examples which include the Cobalt district of Ontario, Jachymov in the Czech Republic, and Freiberg in eastern Germany.

Without previous structural disturbance to cause the fracturing, there would be nowhere for the deposits to be able to form. Nonetheless, the deposits themselves are almost never deformed in any way. This suggests that they are emplaced very late in the geological history of a region.

The vast majority of geologists who have studied these deposits recognize that the veins are hydrothermal, but there is not a single genetic model that has been accepted widely.

Unconformity Uranium Deposits
The unconformity-type deposits are the earth’s principal source of uranium. These deposits form near or at the contact between an overlying sandstone and underlying metamorphic rocks, often metamorphosed shales. The orebodies have the shapes of lens or pods nad they most often occur along fractures in sandstone or in basement rocks. The host rocks very often have disseminated minerals of uranium and show hydrothermal alteration, which can show that the deposits were formed after the rocks. The mineralized bodies can carry small amounts of sulphide minerals like sphalerite, galena, arsenopyrite, and pyrite, as well as cobalt and nickel arsenides.

Due to the fact that this type of deposit is a relatively recent discovery – the first huge discovery of uranium deposits in Saskatchewan and northern Austrailia were found in the late 1960s and early 1970s – geologists even till today have been trading theories as to how these deposits originated. A model that has gotten favor in recent years suggests that fluids with dissolved uranium and other metals, moving through the sandstone, encountered the basement rocks, where the chemical conditions were perfect to cause the metals to precipitate from solution.